Multi-layered anisotropic conductive adhesive having conductive fabric and preparation thereof

ABSTRACT

The present disclosure provides a multi-layered anisotropic conductive adhesive including an upper conductive adhesive layer, a conductive fabric layer with two sides and a lower conductive adhesive layer, wherein one side of the conductive fabric layer is plated with metal, and the total thickness of the multi-layered anisotropic conductive adhesive is 40 to 60 μm. In the application of a flexible printed circuit, reinforced parts, formed by laminating multi-layered anisotropic conductive adhesive with steel or polyimide-type stiffener, can effectively prevent the deformation of installed parts due to warping, and ensure the good hole filling, good direct grounding effect, and good shielding performance. Therefore, the multi-layered anisotropic conductive adhesive of the present disclosure has good electrical properties, good adhesive strength, better tin soldering, reliability and flame resistant. The disclosure further provides a method of producing the multi-layered anisotropic conductive adhesive.

TECHNICAL FIELD

The present disclosure relates to conductive adhesives for printedcircuit boards, especially to a multi-layered anisotropic conductiveadhesive having conductive fabric.

BACKGROUND

As electric and communication products develop, circuit board elementshave been developed towards lighter in weight, thinner in thickness,shorter in length, smaller in size, and higher in integration withbroader and broader frequency band for signal transmission, resulting inmore and more serious electromagnetic interference. In addition,application safety of electronic circuit elements has been taken intoconsideration, and new demands on reliability of ground connection ofcircuit elements in electronic products and variation of circuit boarddesign arise. Currently, conductive adhesive products commonly soldoften have the problem of delamination caused by the conductive adhesiveoverfilling grounding holes, influencing design and mounting of otherelements. Alternatively, the defects of ineffective masking caused bythat the conductive adhesive failing to completely fill, resulting ingaps in the connection parts during reflow soldering.

In addition, most of conductive adhesive products sold currently areformed by dispersing conductive particles in adhesive directly, and theadhesive layer is relatively thick. Therefore, non-uniform dispersion ofparticles will occur during adhesion of the products to a printedcircuit board if curing is insufficient and adhesion is done undernone-uniform pressure, thereby further affecting conductive properties.

Therefore, the present disclosure provides a highly conductivemulti-layered anisotropic conductive adhesive consisting of a pluralityof metal particles in multiple forms and a conductive fabric layer.

SUMMARY

For solving the technical problems, the present disclosure provides amulti-layered anisotropic conductive adhesive having conductive fabric,wherein the conductive adhesive has good electrical properties, adhesivestrength, tin soldering, reliability and flame resistant, has betterconductive effects and adhesive strength compared to common conductiveadhesives, and is more easily produced with a prospect of a broad rangeof applications. In the view of a main application in a flexible printedcircuit board, a reinforced assembly formed by adhering themulti-layered conductive adhesive to a steel sheet or a reinforced boardmade of polyimide can effectively prevent deformation at the mountingposition due to bending, and ensure good hole filling, thereby havingthe effect of directly ground shielding external signal interference.

In order to solve the technical problem described above, the presentdisclosure provides multi-layered anisotropic conductive adhesive havingconductive fabric, which includes: an upper conductive adhesive layerwith a thickness of 20 to 40 μm; a lower conductive adhesive layer witha thickness of 20 to 40 μm, wherein both the upper conductive adhesivelayer and the lower conductive adhesive layer include a plurality ofmetal conductive particles with particle sizes of 2 to 50 μm, and theplurality of metal conductive particles are in at least two shapesselected from the group consisting of dentritic, needle-like, flaky andspherical forms; and a conductive fabric layer having an upper side anda lower side with a thickness of 5 to 30 μm, the conductive fabric layerbeing formed between the upper conductive adhesive layer and the lowerconductive adhesive layer for the multi-layered anisotropic conductiveadhesive to have a total thickness of 40 to 60 μm, wherein at least oneside of the conductive fabric layer is plated with a metal layer.

In one embodiment, the plurality of metal conductive particles haveparticle sizes in a range of 5 to 45 μm.

In another embodiment, the plurality of metal conductive particles haveparticle sizes in a range of 10 to 45 μm.

In one embodiment, both the upper conductive adhesive layer and thelower conductive adhesive layer are thermosetting adhesive layers, eachof which includes an adhesive resin and the plurality of metalconductive particles, wherein each of the upper conductive adhesivelayer and the lower conductive adhesive layer contains the adhesiveresin in an amount of 20 to 75% by weight, the plurality of metalconductive particles in an amount of 25 to 70% by weight, and the weightratio of the plurality of metal conductive particles to the adhesiveresin is from 1:1 to 4:1.

In one embodiment, the conductive fabric layer is fiber cloth, and thefiber cloth can be at least one selected from the group consisting ofgridding cloth, plain weaving fabric and non-woven fabric, wherein thefiber cloth has a plurality of micropores having sizes allowing thesmallest metal conductive particle in the upper conductive adhesivelayer and the lower conductive adhesive layer to pass through the fibercloth.

In another embodiment, each of the micropores in the conductive fabriclayer has a size greater than or equal to 5 μm.

In one embodiment, the metal layer on the surface of the conductivefabric layer can be a copper nickel plating layer, a copper cobaltplating layer, a copper tin plating layer, a copper silver platinglayer, a copper iron nickel plating layer, a copper gold plating layeror a copper plating layer.

In one embodiment, the plurality of metal conductive particles areformed by mixing a plurality of dentritic metal conductive particleswith a plurality of needle-like metal conductive particles and aplurality of flaky metal conductive particles, wherein the weight ratioof the plurality of dentritic metal conductive particles to theplurality of needle-like metal conductive particles is from 1:5 to 5:1,and the weight ratio of the plurality of needle-like metal conductiveparticles to the plurality of flaky metal conductive particles is from1:4 to 4:1.

In one embodiment, the materials forming the plurality of metalconductive particles include conductive alloy particles.

In one embodiment, the adhesive resin is at least one selected from thegroup consisting of an epoxy resin, an acrylic resin, a urethane resin,a silicon rubber resin, a poly-p-xylene resin, a bismaleimide-basedresin, a phenolic resin, a melamine resin, and a polyimide resin.

In one embodiment, two releasable layers each having a thickness of 25to 100 μm are formed below the lower conductive adhesive layer and onthe upper conductive adhesive layer, respectively, wherein each of therelease layers can be a single-sided release film or a double-sidedreleasable film, and the release layers can be fluorine-coated polyesterrelease films, silicone oil-coated polyester strippable films, mattepolyester release films, polyethylene release films or polyethylenelaminated paper layers.

The present disclosure further provides a method for preparing amulti-layered anisotropic conductive adhesive, which includes: mixing aplurality of metal conductive particles having particle sizes in a rangeof 2 to 22 μm with an adhesive resin at a weight ratio of 1:1 to 4:1 toform a mixture, wherein the plurality of metal conductive particles haveat least two shapes selected from the group consisting of dentritic,needle-like, flaky and spherical forms; coating the mixture on aspecified release surface of the release layer to form a lowerconductive adhesive layer; adhering the conductive fabric layer to thesurface of the lower conductive adhesive layer; coating another mixtureformed by mixing a plurality of metal conductive particles with particlesizes of 2 to 22 μm with an adhesive resin at a weight ratio of 1:1 to4:1 onto the other side of the conductive fabric layer, so to form theupper conductive adhesive layer; and adhering a release layer to thesurface of the upper conductive adhesive layer.

In one embodiment, the method further includes pre-curing the lowerconductive adhesive layer after the conductive fabric layer is adhered,and pre-curing the upper conductive adhesive layer after adhering therelease layer to the surface of the upper conductive adhesive layer.

In one embodiment, the mixture is identical to the other mixture.

In one embodiment, the method further includes a rolling step and astrip-forming step to give a product.

The present disclosure provides a multi-layered anisotropic conductiveadhesive to have the upper conductive adhesive layer and the lowerconductive adhesive layer including a plurality of metal conductiveparticles in at least two shapes. Thus, the plurality of metalconductive particles tend to flow in many directions due to the manyshapes thereof, when deformations occur under thermal pressure duringprocessing, resulting in multi-directional highly dispersed distributionof the plurality of metal conductive particles in the conductiveadhesive layer after lamination. Thus, a conductive circuit is formedwith the grounding holes in a flexible board for the upper conductiveadhesive layer and the lower conductive adhesive layer to impart goodanisotropic conductivity, thereby enhancing the conductive propertiesgreatly and reducing grounding resistance value of the flexible board.

In addition, the fibrous or net structure of the conductive fabric layerof the present disclosure facilitates the plurality of metal conductiveparticles in the upper conductive adhesive layer and the lowerconductive adhesive layer to pass through the micropores thereof, so asto achieve conduction between the upper and lower conductive adhesivelayers. Meanwhile, no delamination will occur during surface adhesionprocess of a flexible printed circuit boards due to the good gaspermeability of the conductive fabric layer, thereby effectively solvingthe problems of delamination of the current conductive adhesives andconductive adhesives with introduced metal layers.

By using fiber cloth as the substrate, the conductive fabric layer ofthe present disclosure has good flexibility and wearability to avoiddeformation when the flexible circuit board is thermally pressed due tothe high rigidity of the conductive adhesive, thereby avoiding influenceon properties. Meanwhile, the plurality of metal conductive particles inthe upper conductive adhesive layer and the lower conductive adhesivelayer are thermally pressed to make the adhesive resin flow to achieveanisotropic conductivity, thereby effectively avoiding the disadvantagesof low conductivity of conventional conductive adhesive and theconductive adhesive with introduced metal thin layer(s).

Further, since the surface of the conductive fabric layer of the presentdisclosure is electroplated with metal to form a metal layer, in thecondition of the same conductivity, a relatively lower amount of theplurality of metal conductive particles can be used in the upperconductive adhesive layer and the lower conductive adhesive layer,thereby reducing dust pollution, decreasing cost, and greatly enhancingadhesive strength of the product.

Also, after curing and laminating at high temperature for a period, theanisotropic plurality of metal conductive particles can improve theadhesive resin to achieve the same electricity and mechanical propertyas those achieved after complete cross-linking and curing.

The external electromagnetic wave interference can also be effectivelyshielded, because of the good grounding stability when the conductiveadhesive layer of the present disclosure and metal parts such as a steelboard are covered and adhered onto a printed circuit board to form areinforced part.

Additionally, the metal particles of the present disclosure contain aplurality of conductive alloy particles, which have excellentanti-oxidation and conductivity, and are beneficial for storage anddelivery without affecting physical and chemical properties of theproducts. Therefore, the products have the properties of high stabilityand reliability.

The foregoing merely provides an overview on the technology of thepresent disclosure, and in order to allow a person to more clearlyunderstand on the technical means of the present disclosure and topractice according to the content of the present specification, thepresent disclosure will be described in detail by following Examplesaccompanying the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the structure of the presentdisclosure;

FIG. 2 is a schematic diagram showing conduction of a multi-layeredanisotropic conductive adhesive of the present disclosure; and

FIG. 3 is a schematic diagram showing a stripping force of themulti-layered anisotropic conductive adhesive of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The embodiments of the present disclosure will be illustrated byparticular Examples described below, and anyone skilled in the art caneasily understand the advantages and effects of the present disclosurebased on the content of the present specification.

It should be noted that all of the structures, ratios, sizes and so onshown in the Figures are used for the purpose of illustration of thecontent of the present specification, which are provided forunderstanding and reading by anyone skilled in the art, rather thanlimit conditions for practicing the present disclosure. Therefore, theyhave no substantial meaning in technical view. Any modification ofstructure, alteration of proportion or adjustment of size, which has noinfluence on effects and purposes of the present disclosure, should fallwithin the scope encompassed by technical content described in thepresent disclosure. Meanwhile, words used herein such as “a”, “an”,“upper” and “lower” are merely used for clear description, not forlimiting the implemental scope of the present disclosure. Thus, thealteration or adjustment on the relative relationship without anysubstantial change in the technical content should be considered aswithin the scope of the present disclosure.

In addition, all of ranges and values used herein are inclusive andcombinable. Any value or point within the range described herein, suchas any integer, can be used as the minimum or the maximum value toderive a subrange and the like.

Referencing to FIG. 1, a multi-layered anisotropic conductive adhesive100 includes: an upper conductive adhesive layer 101 with a thickness of20 to 40 μm; an lower conductive adhesive layer 102 with a thickness of20 to 40 μm, wherein both the upper conductive adhesive layer and thelower conductive adhesive layer include a plurality of metal conductiveparticles 1011, and the plurality of metal conductive particles each hasa size of 2 to 50 μm and contains metal conductive particles in at leasttwo shapes selected from the group consisting of dentritic, needle-like,flaky and spherical forms; and a conductive fabric layer 102 with athickness of 5 to 30 μm and an upper side and a lower side, and isformed between the upper conductive adhesive layer 101 and the lowerconductive adhesive layer 103, wherein at least one side of theconductive fabric layer is plated with a metal layer; and themulti-layered anisotropic conductive adhesive has a total thickness of40 to 60 μm.

Typically, the conductive particles in the upper conductive adhesivelayer and the lower conductive adhesive layer are of only one shape, andtend to flow and distribute in one direction upon dispersion andlamination to allow conductivity of the conductive adhesive layer to bein one direction, resulting in poor overall conductivity of theconductive adhesive layer, and thus affecting shielding effect of theconductive adhesive. The plurality of metal conductive particles in manyshapes used in the present disclosure deform under thermal pressingduring their distribution into the adhesive layer, thereby allowing theconductive adhesive layer to impart good anisotropic conductivity andenhancing shielding efficacy.

The conductive fabric layer 102 has a thickness of 5 to 30 μm, whichallows the conductive fabric layer to have excellent flexibility andwearability and improved reliability and shielding efficacy. Theplurality of metal conductive particles in the upper conductive adhesivelayer and the lower conductive adhesive layer cannot be in contact withone another if too thick, resulting in poor contact between theconductive particles in the upper layer and that in the lower layer; andproduction cost will be greatly increased if too thin.

The multi-layered anisotropic conductive adhesive has a total thicknessof 40 to 60 μm. The shielding effect will be poor if the conductiveadhesive layer is too thin; and if the conductive adhesive layer is toothick, the requirement for a thinner product cannot be satisfied and itis not beneficial to coating processing, resulting in increasedproduction cost.

Both of the upper conductive adhesive layer 101 and the lower conductiveadhesive layer 103 are thermosetting adhesive layers, each of whichincludes an adhesive resin 1012 and the plurality of metal conductiveparticles, wherein each of the upper conductive adhesive layer and thelower conductive adhesive layer contains the adhesive resin in an amountof 20 to 75 wt % and the plurality of metal conductive particles in anamount of 25 to 70 wt %, and the weight ratio of the plurality of metalconductive particles to the adhesive resin is 1:1 to 4:1. Theconductivity is poor if the ratio is lower than 1:1, and the high amountof adhesive will cause problem of easily generating a sticky boardduring subsequent operations. If the ratio is higher than 4:1, theproportion of the powder will be too high to dispense, and it can causeinfluences on the close adhesion and adhesive strength. In addition, theupper conductive adhesive layer and the lower conductive adhesive layerof the present disclosure further include some auxiliaries (e.g.,hardener, thickener, and the like) and non-metal conductive particles(e.g., graphite, conductive compounds, and the like).

The viscosity will be too low if the adhesive resin is too little; andif the adhesive resin is too much, the product will be too viscous andthe relative content of the plurality of metal conductive particles isdecreased, resulting in poor conductivity.

In one embodiment, in each of the upper conductive adhesive layer andthe lower conductive adhesive layer, the proportion of the plurality ofmetal conductive particles is 35 to 55 wt %.

The conductive fabric layer is fiber cloth, which is at least oneselected from the group consisting of gridding cloth, plain woven clothand non-woven cloth, wherein the fiber cloth has micropores each with asize larger than that of the smallest metal conductive particles in theupper conductive adhesive layer and the lower conductive adhesive layerto allow the metal conductive particles to pass through the fiber cloth.

In another embodiment, each of the micropores in the conductive fabriclayer has a size greater than or equal to 5 μm.

The metal layer on the surface of the conductive fabric layer 102 can bea copper nickel plating layer, a copper cobalt plating layer, a coppertin plating layer, a copper silver plating layer, a copper iron nickelplating layer, a copper gold plating layer or a copper plating layer.

In one embodiment, the metal layer on the surface of the conductivefabric layer is a copper nickel plating layer or a copper silver platinglayer.

In one embodiment, the plurality of metal conductive particles each hasa size of 5 to 45 μm; in another embodiment, the plurality of metalconductive particles has a size of 10 to 45 μm; wherein the plurality ofmetal conductive particles are formed by mixing a plurality of dentriticmetal conductive particles, a plurality of needle-like metal conductiveparticles and a plurality of flaky metal conductive particles, theweight ratio of the plurality of dentritic metal conductive particles tothe plurality of needle-like metal conductive particles is 1:5 to 5:1,and the weight ratio of the plurality of needle-like metal conductiveparticles to the plurality of flaky metal conductive particles is 1:4 to4:1.

The materials for forming the plurality of metal conductive particlesinclude at least one of single metal conductive particles and conductivealloy particles. In one embodiment, conductive alloy particles arepreferable as the plurality of metal conductive particles.

Among these, the single metal conductive particles can be at least oneselected from the group consisting of gold, silver, copper and nickelparticles, but not limited thereto. The conductive alloy particles canbe at least one selected from the group consisting of Ag—Cu platedparticles, Ag—Au plated particles, Ag—Ni plated particles, Au—Cu platedparticles and Au—Ni plated particles, but are not limited thereto.

The conductive alloy particles have good and conductivity, and theproducts thereof can be stored and delivered without affecting theirphysical properties, resulting in the properties of high stability andreliability of the products.

The adhesive resin is at least one selected from the group consisting ofepoxy resins, acrylic resins, urethane resins, silicone rubber resins,poly-p-xylene resins, bismaleimide-based resins, phenolic resins,melamine resins, and polyimide resins. In one embodiment, the acrylicresins are particularly preferable.

Release layers 104 can each be formed under the lower conductiveadhesive layer 103 and on the upper conductive adhesive layer 101,respectively, and it is not beneficial for subsequent die cutting if therelease layers are too thick or too thin. The release layers can besingle-sided release films or double-sided strippable films, and therelease layers can be fluorine-coated polyester release films, siliconeoil-coated polyester release films, matte polyester release films,polyethylene release films or polyethylene laminated paper layers.

The release films of the release layers are pure white, milk white ortransparent. In one embodiment, a pure white or a milk white releaselayer is particularly preferable, since a pure white or milk whiterelease film has no problem of light reflection under interaction withinfrared ray when engraving a circuit using a digitally-controlledautomatic equipment, thereby quickly and accurately achieving thelocation and operation. In addition, the pure white or milk white colorcan be recognized by a worker, thereby reducing the risk of leaving therelease layer unstripped in the case of manual operation.

The present disclosure further provides a method for preparing themulti-layered anisotropic conductive adhesive, which includes:

Step I: screening the metal conductive particles in various shapes toobtain the particles with desired particle diameters, mixing theobtained metal conductive particles in various shapes uniformly to forma mixture consisting of a plurality of metal conductive particles,wherein the mixing can be performed by ball milling, and the millingrate should not be too high (preferably at a milling rate of 200 to 300rpm), otherwise, the surface alloy layer of the metal particles will bedestroyed. Alternatively, the mixing can be performed by stirring(preferably at a rate of 700 to 2,000 rpm), but mixing at a higher ratewill give a plurality of metal conductive particles with the bettermixing uniformity.

Step II: mixing the adhesive resin and the aforementioned mixture of aplurality of metal conductive particles thoroughly, while adding amixture of a plurality of metal conductive particles, under the samemixing conditions as those in Step I.

Step III: coating the mixture obtained in Step II on the specifiedrelease surface of the release layer to form a lower conductive adhesivelayer.

Step IV: adhering the lower conductive adhesive layer to a conductivefabric layer as support, pre-curing the lower conductive adhesive layerat a temperature which should not higher than the curing temperature ofthe adhesive resin itself, and the present disclosure employs apre-curing temperature between 80□ and 100□, and removing the supportafter pre-curing to form the conductive fabric layer.

Step V: coating the mixture prepared in Step II on the other side of thethin metal layer to form an upper conductive adhesive layer. Of course,another mixture formulated in different composition and proportion canalso be used.

Step VI: curing the upper conductive adhesive layer under the pre-curingconditions in Step IV, then rolling to give final products.

EXAMPLES

Test Method 1: Analysis on Conductivity

A conductivity test was performed on the multi-layered anisotropicconductive adhesive after removing the release film using a high bridgetester. As shown in FIG. 2, after pseudo-adhering a nickel steel platingsheet 200 and a printed circuit board 300 on the surface of the upperconductive adhesive layer 101 and the lower conductive adhesive layer103 respectively, pressing (at a pressure of 100 kgw and a temperatureof 180 □, pre-pressing for 10 sec and pressing for 120 sec) and curing(at temperature of 160 □ for 1 hr), conductive resistance values of thesample before reflow soldering and after three times of reflow solderingwere each examined. The present disclosure was taken as an Example andthe test for electric conductivity of general products by the samemethod was taken as the Comparative Example, and the examinedconductivity results are recorded in Table 1.

Heat resistance during soldering: after pseudo-adhering a nickel steelplating sheet 200 and a printed circuit board 300 on the surface of theupper conductive adhesive layer 101 and the lower conductive adhesivelayer 103 respectively, pressing (at a pressure of 100 kgw and atemperature of 180 □, pre-pressing for 10 sec and pressing for 120 sec)and curing (at a temperature of 160 □ for 1 hr), the sample was placedin a high temperature soldering furnace where occurrences of phenomenaincluding bubbles, streaks, melting, and the like were observed, withreference to the IPC-TM650 2.4.13 soldering test method.

Test Method 2: Analysis on Peeling Strength

The multi-layered anisotropic conductive adhesive after the strippablefilms being removed was tested for its peeling strength using auniversal tensile strength tester. As shown in FIG. 3, afterpseudo-adhering a nickel steel plating sheet 200 and a single-sidedcopper coil-coated substrate 400 on the surface of the upper conductiveadhesive layer and the lower conductive adhesive layer, respectively,pressing and curing, and obtaining the sample for a test for the peelingstrength thereof. The present disclosure was taken as an Example and thetest for peeling strength of general products by the same method wastaken as the Comparative Example, and the tested conductivity resultsare recorded in Table 1.

Example 1: Preparation of a Multi-Layer Anisotropic Conductive AdhesiveHaving Conductive Fabric

A mixture of metal particles in different shapes was prepared byscreening powder of silver copper-plated spherical metal conductiveparticles and silver nickel plated needle-like ones, both having D90particle size of about 45 μm, and agitating and mixing the metalconductive particles described above under a ball milling condition of250 rpm, wherein the weight ratio of the plurality of spherical metalparticles to the plurality of needle-like metal conductive particles was1:1.

Thereafter, an acrylic adhesive resin (RD0351 and RD0352, manufacturedby Asia Electronic Material Co., Ltd.) was added to the aforementionedmixture of metal particles in different shapes, then was mixedthoroughly under a ball milling condition of 250 rpm to form a uniformmixture while adding the mixture of metal particles in different shapes,so as to form a coating mixture consisting of 55% of the acrylicadhesive resin, 25% of the aforementioned mixture of metal particles indifferent shapes, and auxiliaries (RD0223 and RD0339, manufactured byAsia Electronic Material Co., Ltd.) in balance, wherein RD-0223 adjustedthe intermolecular bonding force and dispersing uniformity of theadhesive resin, while RD-0339 adjusted the final viscosity of theadhesive resin mixture, and the addition ratio of RD-0223 to RD-0339 was1:1.

The coating mixture was coated on a designated side of thefluorine-coated polyester release layer to form a lower conductiveadhesive layer with a thickness of 20 μm, then the lower conductiveadhesive layer was adhered onto a conductive fabric layer having acopper nickel plating layer as a support, pre-curing at a temperature of80 □, and after the pre-curing was completely, the support was removedto form the conductive fabric layer with a thickness of 2 μm.

The upper conductive adhesive layer with the same composition as thelower conductive adhesive layer and with a thickness of 20 μm was formedon the other side of the conductive fabric layer by the same procedureof coating and pre-curing.

Physical properties of the multi-layered anisotropic conductive adhesivewere tested and recorded in Table 1.

The preparation methods of multi-layered anisotropic conductiveadhesives of Examples 2-5 and Comparative Examples 1-2 were the same asthat of Example 1, except that the ratio of metal powder to adhesiveresin, mixing weight ratio of metal powder, types of metal powder, kindsof metal layers of the conductive fabric, and the thicknesses of theupper and the lower conductive adhesive layers were altered as shown inTable 1. Physical properties of the multi-layered anisotropic conductiveadhesives were tested and recorded in Table 1.

TABLE 1 Thickness Type of Thickness of the Thickness the metal of theupper of the layer on lower Type of conductive Metal Adhesive conductivethe conductive the metal adhesive powder resin fabric conductiveadhesive conductive Shapes of the metal layer (μm) (wt %) (wt %) layer(μm) fabric layer (μm) particles conductive particles Ex. 1 20 25 55  5Cu—Sn 20 Ag—Cu, spherical/needle-like/ Ag—Ni Ex. 2 25 35 55 15 Cu—Ag 25Ag—Ni, dentritic/needle-like Ag—Au Ex. 3 30 55 40 10 Cu 30 Ag—Au,needle-like/flaky Ag—Cu Ex. 4 40 50 40 20 Cu—Sn 40 Ag, spherical/flakyNi Ex. 5 25 70 20 30 Cu—Co 25 Ni, flaky/spherical Ag—Cu Comp. Ex. 1 6065 — — — — — Comp. Ex. 2 40 70 — — — — — Thermal Weight ratio ofResistance Resistance resistance Peeling the metal after after three tostrength conductive baking SMT soldering (kg particles (mOhm) (mOhm) tinweight/cm) Ex. 1 spherical:needle- 86 75 320□ 30 s 2.45 like = 1:1passed Ex. 2 dentritic:needle- 62 57 320□ 15 s 2.37 like = 1:1 passedEx. 3 needle-like:flaky = 30 28 310□ 60 s 2.42 1:1 passed Ex. 4spherical:flaky = 52 46 310□ 60 s 2.30 1:1 passed Ex. 5 flaky:spherical= 45 41 300□ 60 s 1.95 1:1 passed Comp. Ex. 1 — 115 118 300□ 30 s 1.78passed Comp. Ex. 2 — 102 100 300□ 30 s 1.60 passed

In Table 1, the upper conductive adhesive layer and the lower conductiveadhesive layer have the same composition.

It can be seen from the above Table 1 that, the multi-layeredanisotropic conductive adhesive has good conductive effects and thermalresistance tin soldering, as well as good adhesive strength.

The above Examples are provided for purpose of illustration only, andare not intended to limit the present disclosure. Anyone skilled in theart can make modification and alteration on above Examples withoutdeparting from the spirits and scope of the present disclosure. Thus,the scope the present disclosure is defined by accompanying claims, andshould be encompassed in the technical content disclosed in the presentdisclosure, as long as it has no influence on the effects and purpose ofthe present disclosure.

What is claimed is:
 1. A multi-layered anisotropic conductive adhesive,comprising: an upper conductive adhesive layer having a thickness offrom 20 μm to 40 μm; a lower conductive adhesive layer having athickness of from 20 μm to 40 μm, wherein the upper conductive adhesivelayer and the lower conductive adhesive layer each comprise a pluralityof metal conductive particles having particle sizes in a range of from 2μm to 50 μm, and wherein the plurality of metal conductive particleshave at least two shapes selected from the group consisting ofdentritic, needle-like, flaky and spherical forms; a conductive fabriclayer having an upper side and a lower side with a thickness of from 5μm to 30 μm, the conductive fabric layer being formed between the upperconductive adhesive layer and the lower conductive adhesive layer forthe multi-layered anisotropic conductive adhesive to have a totalthickness of from 40 μm to 60 μm; and a metal layer coated on at leastone of the upper side and the lower side of the conductive fabric layer.2. The multi-layered anisotropic conductive adhesive of claim 1, whereinthe plurality of metal conductive particles are in an amount of from 25wt % to 70 wt % in each of the upper conductive adhesive layer and thelower conductive adhesive layer.
 3. The multi-layered anisotropicconductive adhesive of claim 1, wherein the upper conductive adhesivelayer and the lower conductive adhesive layer are composed ofthermosetting adhesive, and the upper conductive adhesive layer and thelower conductive adhesive layer each comprise an adhesive resin.
 4. Themulti-layered anisotropic conductive adhesive of claim 3, wherein theadhesive resin is in an amount of from 20 wt % to 75 wt % in each of theupper conductive adhesive layer and the lower conductive adhesive layer.5. The multi-layered anisotropic conductive adhesive of claim 3, whereina weight ratio of the plurality of metal conductive particles to theadhesive resin is from 1:1 to 4:1.
 6. The multi-layered anisotropicconductive adhesive of claim 3, wherein the adhesive resin is at leastone selected from the group consisting of an epoxy resin, an acrylicresin, a urethane resin, a silicone rubber resin, a poly-p-xylene resin,a bismaleimide-based resin, a phenolic resin, a melamine resin, and apolyimide resin.
 7. The multi-layered anisotropic conductive adhesive ofclaim 1, wherein the conductive fabric layer is composed of fiber clothselected from the group consisting of gridding cloth, plain weavingfabrics and non-woven fabrics.
 8. The multi-layered anisotropicconductive adhesive of claim 7, wherein the fiber cloth has a pluralityof micropores having sizes allowing for the smallest one of the metalconductive particles in the upper conductive adhesive layer and thelower conductive adhesive layer to pass therethrough.
 9. Themulti-layered anisotropic conductive adhesive of claim 1, wherein themetal layer on the conductive fabric layer is a copper nickel platinglayer, a copper cobalt plating layer, a copper tin plating layer, acopper silver plating layer, a copper iron nickel plating layer, acopper gold plating layer or a copper plating layer.
 10. Themulti-layered anisotropic conductive adhesive of claim 1, wherein theparticle sizes of the plurality of metal conductive particles are in arange of from 5 μm to 45 μm.
 11. The multi-layered anisotropicconductive adhesive of claim 1, wherein the plurality of metalconductive particles are composed of a mixture including a plurality ofdendritic metal conductive particles, a plurality of needle-like metalconductive particles and a plurality of flaky metal conductiveparticles.
 12. The multi-layered anisotropic conductive adhesive ofclaim 11, wherein a weight ratio of the plurality of dentritic metalconductive particles to the plurality of needle-like metal conductiveparticles is from 1:5 to 5:1.
 13. The multi-layered anisotropicconductive adhesive of claim 11, wherein a weight ratio of the pluralityof needle-like metal conductive particles to the plurality of flakymetal conductive particles is from 1:4 to 4:1.
 14. The multi-layeredanisotropic conductive adhesive of claim 1, wherein the plurality ofmetal conductive particles are composed of a material comprisingconductive alloy particles.
 15. The multi-layered anisotropic conductiveadhesive of claim 1, further comprising two release layers formed belowthe lower conductive adhesive layer and on the upper conductive adhesivelayer, respectively.
 16. The multi-layered anisotropic conductiveadhesive of claim 15, wherein the two release layers each have athickness of from 25 μm to 100 μm.
 17. The multi-layered anisotropicconductive adhesive of claim 15, wherein the release layers are each asingle-sided release film or a double-sided release film, and at leastone of the release layers is a fluorine-coated polyester release film, asilicone oil-coated polyester release film, a matte polyester strippablefilm, a polyethylene release film or a polyethylene laminated paperlayer.
 18. A method for preparing the multi-layered anisotropicconductive adhesive of claim 1, comprising: mixing the plurality ofmetal conductive particles having particle sizes in a range of from 2 μmto 22 μm with an adhesive resin at a weight ratio of from 1:1 to 4:1 toform a mixture, wherein the plurality of metal conductive particles arein at least two shapes selected from the group consisting of dentritic,needle-like, flaky and spherical forms; coating the mixture on aspecified release surface of a release layer to form the lowerconductive adhesive layer; adhering the conductive fabric layer to asurface of the lower conductive adhesive layer; coating another mixtureformed by mixing the plurality of metal conductive particles havingparticle sizes in a range of from 2 μm to 22 μm with the adhesive resinat a weight ratio of from 1:1 to 4:1 onto the other side of theconductive fabric layer to form the upper conductive adhesive layer; andadhering the release layer to a surface of the upper conductive adhesivelayer.
 19. The method of claim 18, further comprising pre-curing thelower conductive adhesive layer after adhering the conductive fabriclayer to the surface of the lower conductive adhesive layer, andpre-curing the upper conductive adhesive layer after adhering therelease layer to the surface of the upper conductive adhesive layer. 20.The method of claim 18, wherein the mixture is identical to the anothermixture.